The use of brake disc stacks in aircraft braking systems is well known. Interleaved discs alternately splined to the wheel and axle of the aircraft are forced together to achieve the frictional braking action. Typically, brake pistons are provided within the brake housing and caused to act against a pressure plate which is in turn urged against the stack. It is well known that as the discs wear the required stroke of the pistons increases. Unless the pistons are of a telescopic nature, the length of the piston assembly must be at least equal to the maximum travel distance of the piston during the life of the brake disc stack. Telescopic pistons allow greater piston travel in a compact housing, while maximizing the wear obtained from the discs of the stack.
While telescopic brake piston assemblies have previously been known, the piston output force for a given input force has been found to vary as a function of the piston extension. In those brake piston assemblies in which concentric pistons are sequentially actuated, it has been found that the relationship between input pressure and output force with respect to the brake piston is a function of the stage being actuated at that point in the life of the brake disc stack. Accordingly, the braking action resulting from a pilot's braking effort will change during the useful life of the brake disc stack. Of course, such is most undesirable.
There is accordingly a need in the art for a telescopic brake piston which demonstrates a constant and consistent relationship between the input pressure and the output force, while allowing maximum extension of the telescopic piston to maximize brake wear, while maintaining the same in a housing of minimal size.